Fig. 2. Inhibition of transcription in early embryos extends sensitivity to dn-Xtcf3. (A) Embryos were exposed to actinomycin D (ActD) from the two-cell stage to either the eight-cell or 16-cell stage, and dn-Xtcf3 RNA was then injected into all four dorsal blastomeres, and phenotype was scored as in Fig. 1. (B) ßTGR RNA was injected into two dorsal blastomeres at the four-cell stage. Dexamethasone (dex) was then added to embryo culture medium at the four-cell or 32-cell stage. Where indicated, embryos were cultured in ActD containing medium from the four-cell stage to the 32-cell stage and then transferred to dex-containing medium until stage ten. Phenotypes were scored at tailbud stage.